1. Field of the Invention
The present invention relates to a suspension of a vehicle wheel in a vehicle such as an automobile, and more particularly, to a suspension device of the type constructed by a combination of a plurality of links.
2. Description of the Prior Art
As a very common structure of the link type vehicle wheel suspension it is known, as diagrammatically shown in FIG. 1, to support a carrier 10 for supporting a vehicle wheel 12 to be rotatable about a central axis of rotation thereof such as A by an upper arm such as an A-type arm 16 connected with an upper portion of the carrier 10 at an outboard end thereof via a pivot joint 18 to be pivotable relative to one another about at least one substantially horizontal and longitudinal axis of revolution also connected with a body 24 of the vehicle at an inboard end thereof via pivot joints such as 20 and 21 provided at the free ends of the two leg portions of the A-type arm to be pivotable relative to one another about a substantially horizontal and longitudinal axis of revolution, and a lower arm 26 connected with a lower portion of the carrier 10 at an outboard end thereof via a pivot joint 28 to be pivotable relative to one another about at least one substantially horizontal and longitudinal axis of revolution and also connected with the body 24 of the vehicle at an inboard end thereof via a pivot joint 30 to be pivotable relative to one another about a substantially horizontal and longitudinal axis of revolution and to have at least a certain small freedom of revolution about a substantially vertical axis of revolution, wherein forward and rearward movements of the outboard end of the lower arm 26 are restricted by a strut member 48 firmly connected with an outboard portion of the lower arm 26 at a rear end thereof and connected with the body 24 of the vehicle at a front end thereof via a pivot joint 54 to be pivotable relative to one another about a substantially horizontal and longitudinal axis of revolution. When the vehicle wheel supported by such a suspension device is a steering vehicle wheel, the carrier 10 is also pivotable relative to the upper arm 16 and the lower arm 26 about a substantially vertical axis of revolution via the pivot joints 18 and 28 which may be ball joints, and the carrier 10 is steered by a knuckle arm 32 mounted thereto being operated by a steering tie rod not shown in the figure.
In such a suspension device, in order to obtain a condition that an instant center of movement of the vehicle wheel is stably maintained at a certain point in the bounding and rebounding movement of the vehicle wheel so that the bounding or rebounding of the vehicle wheel does not cause any abrupt change of orientation of the axis of rotation of the vehicle wheel which would cause a dynamic instability due to the Coriolis' effect of the like, the link mechanism constructed by the carrier 10, the upper arm 16, the lower arm 26, the strut member 48 and the vehicle body 24 is generally so arranged that a phantom straight line such as K passing the pivot points 30 and 54 traverse substantially the axis of revolution in the pivotal connection between the upper arm 16 and the vehicle body 24 which is substantially horizontal and longitudinal as indicated by H at a point such as O which provides the instant center of the bounding and rebounding movement of the vehicle wheel. Herein it is conditioned that the line K traverses substantially the line H, because although two straight lines having different inclinations will exactly traverse one another in a plane geometry, in a three dimensional geometry applied to an actual product of suspension device, it requires a very high precision for any two straight lines to traverse exactly one another beyond a degree practically available and enough for certain objects, functions and advantages desired to be accomplished. Therefore, the concept of "substantially traversing" is used with regard to two straight lines in the present application to provide an allowance for an exact geometric traversing of two straight lines within a range which does not substantially affect the objects, functions and advantages of the invention.
When the vehicle wheel supported by such a suspension device is a front vehicle wheel, it is desirable that the instant center of the bounding and rebounding movement of the vehicle wheel, i.e., O, is relatively close to the axis of rotation of the vehicle wheel, A, from the view point of improving the anti-nose diving performance in the braking of the vehicle, in which the mass of a front portion of the vehicle body under the inertia would ride on the braked vehicle wheel by turning about a point of contact T of the vehicle wheel with the ground surface G as supported from the vehicle wheel by a phantom arm R expanded between the point T and the point O, as if the mass of the front portion of the vehicle body were centralized at the point O, thereby generating a greater force for pushing up the front portion of the vehicle body against the nose diving as an angle of inclination j of the phantom arm R from the ground surface G is greater. In order to dispose the point O relatively close to the center of the vehicle wheel, A, as is more readily understood in FIG. 3 showing also diagrammatically the suspension mechanism shown in FIG. 1 as viewed from the inboard side thereof, the pivot joint 30 is required to be as high as possible, while the pivot joint 54 is required to be as low as possible. However, it is often difficult to dispose the pivot joint 30 as high as required because of certain interference thereof with other parts of the vehicle such as a steering gear box, particularly when the vehicle wheel is a steering vehicle wheel. On the other hand, it decreases the bottom height of the vehicle to lower the pivot joint 54.